Pneumomediastinum and surgical emphysema

Written by the X-Ray Atlas editorial team from the sources listed below · Medical review pending · Updated 24 October 2026 · Level: Intermediate

Pneumomediastinum is gas within the mediastinum. Surgical (subcutaneous) emphysema is gas in the soft tissues of the chest wall and neck. They often occur together, because gas tracks freely along tissue planes between the neck, mediastinum, chest wall and retroperitoneum. In a young person after coughing, vomiting or an asthma attack, pneumomediastinum is usually benign and settles on its own. After forceful vomiting, chest trauma or an instrumentation procedure, it can be the first sign of a ruptured oesophagus or airway, which is life-threatening. The film's job is to recognise the gas, tell it apart from pneumothorax and pneumopericardium, and prompt the right next step.

1. How gas gets into the mediastinum

The most common route in spontaneous pneumomediastinum is the Macklin effect: a rise in alveolar pressure ruptures small alveoli, and the gas tracks along the sheaths of the bronchi and vessels back to the hila and into the mediastinum. Other routes are direct: a tear in the trachea, bronchi or oesophagus, gas tracking down from the neck (after dental or facial injury), or up from the retroperitoneum (after bowel perforation). From the mediastinum, gas spreads up into the neck and chest wall, and can rupture into the pleura to cause a pneumothorax.

2. Signs of pneumomediastinum

The key is a thin line of tissue outlined by gas on both sides. Look along the mediastinal borders, around the heart and into the neck, and use the lateral film if one is available.

• Streaky lucencies along the mediastinum, outlining the aortic knob, the heart borders and the trachea, extending up into the neck.
• A thin white line parallel to the left heart border, which is the mediastinal pleura lifted away by gas.
• Continuous diaphragm sign: gas beneath the heart outlines the central part of the diaphragm, so the two hemidiaphragms appear joined in one continuous line. Normally the heart obscures this segment.
• V sign of Naclerio: a V-shaped lucency at the lower left mediastinum, between the descending aorta and the left hemidiaphragm. It is classically associated with oesophageal rupture.
• Ring-around-the-artery sign: on the lateral, gas encircles the right pulmonary artery.
• Tubular artery sign: gas outlines a major artery, such as the aorta or a brachiocephalic branch.
• Double bronchial wall sign: gas on both sides of a bronchial wall makes it unusually distinct.
• Thymic sail (spinnaker sail) sign in children: the thymus is lifted away from the heart by gas.

3. Pneumopericardium and pneumothorax: telling them apart

Feature	Pneumomediastinum	Pneumopericardium	Medial pneumothorax
Extent	Extends above the heart, along the great vessels and into the neck	Surrounds the heart but stops at the pericardial reflection at the root of the great vessels	Lies along the lung edge, often with a visible visceral pleural line elsewhere
Change with position	Does not move much	Moves with patient position (gas rises)	Moves to the non-dependent part of the pleural space
Under the heart	Continuous diaphragm sign	Gas may outline the inferior heart border	Usually no

Pneumopericardium is rare in adults, occurring mostly after trauma, surgery or ventilation. A large volume under tension can cause cardiac tamponade.

Also distinguish the Mach band effect: a thin dark line along the heart border caused by visual perception at an edge, not by gas. A Mach band has no white line (pleura) on its lateral side.

4. Surgical emphysema

• Streaky or bubbly lucencies in the soft tissues of the chest wall, axillae and neck.
• Gas between muscle fibres of pectoralis major creates a striated, fan-like pattern sometimes called the "ginkgo leaf" sign.
• It can spread to the face, eyelids, scrotum and abdominal wall.
• It is rarely harmful in itself, but it can hide an underlying pneumothorax, and extensive surgical emphysema suggests an ongoing air leak.

Common causes include a pneumothorax with a chest drain, especially a drain whose side hole lies outside the pleura or that has become blocked (see chest drain position), rib fractures that tear the lung (see chest trauma), and barotrauma during ventilation.

5. Causes

• Spontaneous: typically young adult men, often after coughing, vomiting, exercise, Valsalva, or inhaled drug use. Usually benign.
• Asthma and other airways disease: see COPD and airways disease.
• Mechanical ventilation (barotrauma).
• Trauma: blunt or penetrating chest and neck injury, including tracheobronchial tears.
• Iatrogenic: endoscopy, oesophageal dilatation, bronchoscopy, intubation (see ETT position), dental and surgical procedures.
• Oesophageal rupture, including Boerhaave syndrome.
• Gas from below: retroperitoneal perforation of the bowel can track up into the mediastinum. See pneumoperitoneum.
• Infection with gas-forming organisms (rare, but serious: mediastinitis).

6. Boerhaave syndrome

Boerhaave syndrome is spontaneous full-thickness rupture of the oesophagus, usually of the lower left wall, after forceful vomiting or retching. The classic clinical picture is vomiting followed by severe chest or upper abdominal pain, and sometimes surgical emphysema. The chest X-ray may show:

• pneumomediastinum, sometimes with the V sign of Naclerio;
• a left pleural effusion or hydropneumothorax;
• surgical emphysema in the neck;
• mediastinal widening.

The film may be normal early. Untreated oesophageal rupture leads to mediastinitis and sepsis with high mortality. If it is suspected, the next test is urgently arranged CT, usually with oral water-soluble contrast, and early surgical review.

7. Next steps

• Look for a pneumothorax, which may need treatment in its own right. See pneumothorax.
• Fit the gas to the story. A well young adult after coughing, with no vomiting, chest trauma or recent procedure, and no signs of sepsis, is likely to have benign spontaneous pneumomediastinum, usually managed conservatively after senior assessment.
• CT is the test when oesophageal or airway injury is possible: after forceful vomiting, trauma, endoscopy, or when the patient is unwell, febrile or has a pleural effusion.
• In ventilated patients, new pneumomediastinum is a warning sign of barotrauma and may precede a tension pneumothorax.

Red flags: act now

What to focus on, by role

Role	Priorities
Medical student	The main signs (streaky lucency, continuous diaphragm, Naclerio's V), the difference from pneumopericardium, and Boerhaave syndrome.
Nurse	Recognise crackling under the skin (crepitus) and spreading swelling around a drain or after a procedure; report it.
Junior doctor	Take the history that separates benign from dangerous causes, look for pneumothorax, and get CT and senior review when rupture is possible.
Radiographer	Include the neck where possible; a lateral can show the ring-around-the-artery sign.
Advanced / FRCR	Subtle signs, Mach bands, pneumopericardium, and gas tracking from the retroperitoneum.

Practise on real chest X-rays →

References

1. Bejvan SM, Godwin JD. Pneumomediastinum: old signs and new signs. AJR 1996;166(5):1041–1048.
2. Radiopaedia. Pneumomediastinum. radiopaedia.org
3. Roberts ME, et al. British Thoracic Society Guideline for pleural disease. Thorax 2023;78(Suppl 3):s1–s42. thorax.bmj.com
4. Royal College of Radiologists. iRefer. irefer.org.uk

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